Matter is anything that occupies space and has mass.
It can be sensed and measured.
Question: Is everything in the universe matter? No.
The Particle Model of Matter
Two historical concepts about matter:
Concept 1: Matter is continuous. It can be subdivided forever; there is no smallest particle.
Concept 2: Matter is NOT continuous. Subdividing matter must eventually stop at the smallest particle, leading to the particle theory of matter.
How big are these particles? Very, very tiny.
A useful intuition: 106 particles laid side-by-side would not be as long as the thickness of a sheet of paper.
What are they called? These smallest particles are called atoms.
Aristotle thought atoms had no size at all.
We can image atoms with the Scanning Tunneling Microscope (STM).
Particle Model Evidence
A good model should match real-life observations.
Examples of diffusion-based mixing:
Dissolving sugar into tea
Dissolving cherry drink mix into water
Indirect observation of particle motion:
The mixing seen in diffusion is caused by random movement of particles.
This motion was first observed in Brownian motion by Robert Brown.
The diffusion/motion evidence supports the idea that matter is made of tiny particles in random, constant motion (Kinetic-Molecular Theory).
Kinetic-Molecular Theory
Matter is composed of tiny particles in random, constant motion.
This motion explains diffusion and many other phenomena.
Atoms
Atom: Basic particle of matter.
Made up of three main subatomic particles:
Protons
Neutrons
Electrons
Location:
Protons and neutrons are in the nucleus and account for almost all the atom’s mass.
Electrons are outside the nucleus and account for the atom’s volume.
Subatomic Particles: Details
Protons have a positive charge (+).
Neutrons have no charge and have roughly the same mass as a proton.
Electrons have a negative charge (−) and very tiny mass.
Molecules
Molecules are formed whenever atoms bond together.
Molecules usually do not have a net charge.
Ions
Ions are formed when atoms gain or lose electrons.
If atoms lose electrons, positive ions (cations) form.
If atoms gain electrons, negative ions (anions) form.
What is "mixing" due to particle motion?
1. Diffusion
2. Boiling
3. Freezing
4. Melting
Answer focus: diffusion is the mixing caused by particle motion.
True/False Practice
A molecule consists of atoms chemically bonded together. True.
Classifying Matter
Categories:
Matter
Pure substances
Mixtures
Pure Substances, Elements, and Compounds
Pure substances contain only one kind of matter.
Elements: All atoms are the same.
Compounds: Made up entirely of the same molecules or ions and have a fixed ratio of elements.
Common chemical symbols and formulas:
Sodium chloride: extNaCl
Water: extH2O
Glucose: extC6H12O6
Calcium carbonate: extCaCO3
Uranium: symbol varies by isotope, but as an element it is a pure substance.
Organic vs Inorganic Compounds
Organic compounds: contain carbon and are typically associated with living things.
Inorganic compounds: do not contain carbon (with some exceptions).
Examples:
Inorganic: water (H2O), table salt (NaCl)
Mixtures
Mixtures are combinations of substances that are physically placed together and are not bonded.
No fixed ratio between components.
Types of Mixtures
Homogeneous mixtures (uniform composition):
Particles are about the same size; separate types of particles are not usually visible; called solutions.
Examples: saltwater, alloys, air, gasoline, 14-karat gold, seawater, chocolate cake (note: some lists vary in examples).
Heterogeneous mixtures (nonuniform composition):
Separate types of particles can often be seen.
Examples: soil, vegetable stew, wood, concrete, granite, blood (depending on context), chocolate cake (in some lists).
Pure Substances vs Mixtures: Quick Reference
Pure Substances:
Elements: All atoms the same.
Compounds: Made of the same molecules/ions with a fixed elemental ratio.
Mixtures:
Variable composition; separated physically; include homogeneous and heterogeneous types.
States of Matter
Three fundamental states: solid, liquid, gas.
Additional states discussed: Plasma, Bose-Einstein Condensate (BEC), Quark-Gluon Plasma.
Solids
Characteristics:
Particles are locked in place; rigid; definite shape.
Low kinetic energy.
Not very compressible; definite volume.
Some solids are crystalline (ordered pattern); others are amorphous (no long-range order).
Also note there is a distinction: crystalline solids have orderly patterns; amorphous solids lack a clear pattern; there are also heterogeneous solids with no single order.
Liquids
Characteristics:
Particles can flow and move past one another; no definite shape.
Higher kinetic energy than in solids.
Not very compressible; definite volume.
Viscosity: a property describing how thick or thin a liquid is.
A viscous liquid has high attraction between particles and flows slowly.
Viscosity decreases as temperature increases.
Lubricants: liquids that reduce friction.
Gases
Characteristics:
Particles are separate from one another and have no definite volume or shape.
Gases are highly compressible due to space between particles.
Particles move very fast and have high kinetic energy, allowing them to overcome attractive forces.
Gases mix readily because their particles are not locked in place.
Fluids
Definition: liquids and gases (substances that have the ability to flow).
Behavior:
Gases expand to fill their container; liquids do not.
Both gases and liquids will mix because particle movement allows mixing.
Warmer substances mix faster due to increased particle motion.
Pressure arises from particles colliding with container walls.
Special States of Matter
Plasma: hot, ionized gas.
Bose-Einstein Condensate (BEC): a very cold, “super-sized” atom made up of many regular atoms.
Quark-Gluon Plasma: a super hot plasma with no atoms present at that temperature.
Quick True/False and Concept Checks
For a molecule to be a molecule of a compound, not all bonded atoms need to be the same element. False (a compound consists of at least two different elements bonded together).
Oxygen is an element.
Tomato juice is a heterogeneous mixture.
Sweetened tea is a homogeneous mixture (a solution).
A homogeneous mixture is also called a solution.
Changes in Matter: Physical vs Chemical vs Nuclear
Physical Properties: can be observed or measured without changing the kind of matter; describes how a substance exists by itself. Examples: color, density, size, shape, hardness, conductivity.
Physical Changes: a change in a physical property; the substance remains the same kind of matter. Examples: cutting paper, freezing water, evaporating alcohol, squeezing a gas.
Chemical Properties: observed only when the substance changes into another substance; describes how the substance reacts with other matter.
Chemical Changes: bonds between atoms break and new bonds form; the identity of the substance changes; new kinds of matter are formed. Examples: burning, rusting, reacting. Note: Kevlar’s strength can be reduced in water or UV light because some bonds break.
Nuclear Changes: changes in the nucleus (protons or neutrons) which alter the element itself; unlike physical or chemical changes, nuclear changes change the identity of the element. Nuclear changes follow conservation laws just like other changes.
Sodium and Salt: Practical Note
Sodium is dangerous in pure form, but salt (sodium chloride) is safe to consume.
Explanations include body not reacting with sodium in salt, properties of compounds differ from their elements, and the body has protective mechanisms against sodium.
Phase Changes (Changes of State)
When matter changes from one state to another, phase changes occur; this can involve two or more states present at the same time (phase change).
As particle vibration speed increases, temperature rises; temperature is the average kinetic energy.
During a phase change, the substance’s temperature remains constant; energy goes into or out of bonds.
Melting: solid to liquid.
Occurs when enough energy is added for particles to overcome attractions; at the melting point particles can flow over one another.
The melting point of a mixture is not a single temperature but depends on the proportions of the particles.
Freezing: liquid to solid; energy is removed until attraction between particles dominates.
Evaporation: liquid to gas at the surface when particles gain enough energy to overcome attractions.
Boiling: vaporization that occurs throughout the liquid when enough energy is available to overcome attractive forces; the boiling point (bp) changes with pressure; vapor is a gas with higher energy and can exert pressure like any gas.
Quick States and Concepts Review Questions
In solids, which force is greater? Options given: kinetic energy vs attraction; Answer: attraction dominates, giving solids their structure.
Why does a solid keep its shape? Likely due to strong interparticle attraction and low kinetic energy (crystal lattice effects in many solids).
Why does a liquid flow? Because there is enough kinetic energy for particles to slide past one another.
Why does a liquid keep its volume? Because particles are still fairly close and attractions hold them together.
Why does a gas not keep its shape? Because there is too much kinetic energy and space to move, allowing expansion.
In gases, which force is greater? Kinetic energy vs attraction; generally kinetic energy dominates.
What do a solid and a liquid have in common? Atoms touch; both have some degree of attraction between particles.
What do liquids and gases have in common? Both can expand to fill containers and can flow; both involve particle motion.
Which is not a state of matter? Gel is not a standard state of matter; Plasma is a state.
Do boiling and evaporation mean the same thing? Not exactly; boiling occurs throughout the liquid at a specific temperature; evaporation occurs at the surface at any temperature.
Increasing temperature increases: speed of molecules (not size of molecules or number of molecules or brightness).
What temperature is halfway between freezing and boiling for water? 50ext°C.
Key Formulas and Notations
Particle count intuition for scale: 106 particles can be used to illustrate atomic scale sizing comparisons.
Chemical formulas presented in standard notation, e.g., extNaCl,extH2O,extC6H12O6,extCaCO3.
General statements about energy and phase changes are qualitative rather than numerical equations in this transcript, but the concepts involve energy transfer and phase-dependent properties.
Connections to Foundational Principles and Real-World Relevance
The particle model provides a basis for understanding matter from everyday substances (water, sugar, salt) to materials engineering ( alloys like 14-karat gold ) and modern physics states (plasma, BEC, quark-gluon plasma).
The distinction between pure substances vs mixtures informs chemistry, environmental science, pharmacology, and materials science—for example, the safety and behavior of salts, acids, and solvents.
Phase changes underpin many industrial processes (melting, freezing, boiling, distillation) and everyday phenomena (ice formation, cooking, evaporation).
Understanding physical vs chemical vs nuclear changes helps predict when a substance will change identity, reactivity, or stability, which is crucial for safety, synthesis, and material design.
Ethical, Philosophical, and Practical Implications
Historical ideas about matter (continuous vs atomic) show how scientific models evolve with evidence, highlighting the importance of empirical testing.
The safety implications of handling elements and compounds (e.g., sodium, radioelements) reflect the need for proper education and protective measures.
The concept that properties of compounds differ from properties of their elements underlines the importance of studying systems holistically rather than judging by parts alone.